Method for accelerating natural weathering of paint and other polymeric materials



United States Patent 3,501,942 METHOD FOR ACCELERATING NATURAL WEATHERING 0F PAINT AND OTHER POLYMERIC MATERIALS Emerson B. Fitzgerald, Wilmington, Del., Mark P. Morse, Jr., Springfield, Pa., Herman L. Wagner, Livingston, N.J., and Anne Willard, Pittsford, Vt., assignors to E. I. do Pout de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Feb. 1, 1967, Ser. No. 613,139 Int. Cl. Gtlln 25/02 US. Cl. 73-15.4 4 Claims ABSTRACT OF THE DISCLOSURE A method for simulating and accelerating the natural weathering of polymeric materials, especially paint, in which samples are subjected to cycles of wetting with Water, drying and exposure to a particular kind of radiant energy.

BACKGROUND OF THE INVENTION This invention relates to a method for simulating and accelerating the natural weathering of paint and other polymeric materials.

To those who manufacture paint and other polymeric materials and to those who use these things, information on how they will bear up under natural weather conditions is of prime importance. From such information the manufacturer learns if his product needs improvement; the user learns what to expect from the product he has just purchased. It is obviously impractical to gather this information by exposing the product to natural weathering because meaningful results might not be gotten for one or more years. So there is need for a method which not only simulates but also accelerates natural weathering so that one can get the information he needs in time for it to be of some value to him.

In years past, many such methods have been suggested and tried but have failed to give the acceleration and the close correlation needed between simulated and natural results. The method of this invention now provides both acceleration and correlation. By using the method, one can accelerate natural weathering by as much as 40 times and yet get results which correlate well with those obtained from exposure to natural conditions, particularly Florida weather.

SUMMARY OF THE INVENTION The method of the invention, in brief, comprises subjecting a sample to the following steps:

(1) Wetting the sample with a specified amount of Water and allowing the sample to remain wet, while keep ing it from direct exposure to radiant energy, for a specified time, within a specified temperature range; and then (2) Directly exposing the sample to a specified amount of a particular type of radiant energy, while keeping the temperature of the sample within a specified temperature range, thereby drying the sample surface.

An apparatus especially suited for carrying out the method is described in copending application Ser. No. 613,284, filed Feb. 1, 1967. The disclosures of that application are incorporated into this one for the purpose of describing the apparatus.

In that apparatus, samples are subjected to the conditions of the method automatically. In addition, radiation step (2) is interrupted and the sample subjected to the following additional steps:

(3) Again keeping the sample from direct exposure to radiant energy, for a specified time, within a specified temperature range; and then "ice (4) Completing exposure of the sample to the radiant energy, while keeping the sample within a specified temperature range.

In the apparatus, means are also provided for drying the sample when it is partially through the first or second radiation step. These means can be a heat source such as an infra-red lamp or a short blast of air across the sample surface.

This apparatus can also be set so that the methods time requirements, the amount of water deposited and the total irradiation fall Within predetermined limits to provide preferred methods (A) and (B). Method (A) is preferred for its high acceleration factor and (B) is preferred for its close correlation with results obtained from natural Florida exposure. Both methods will be elaborated upon in the more detailed description of the general method which follows:

Phase 1 In Phase 1 the sample is uniformly Wetted by water supplied through nozzles. If a deposition of mist is desired, spray from the nozzles can be blown by fans onto the sample, or mist can be supplied by an atomizer.

It is important that the water he demineralized water like that obtained by passing tap water through an ion exchange column.

It is also important that the amount of water deposited on each sample be equivalent to about 003-015 inch of rainfall. This rainfall equivalent can be determined by first passing a piece of blotting paper the same size as a sample past the nozzles and then measuring its weight gain in grams. This weight gain is translated directly into volume (expressed in cubic centimeters) and rainfall equivalent is then computed according to the formula Inches of water= L sample area in cm 2.54

While it is being wetted, and for a time afterward, the sample is kept from direct exposure to radiant energy.

Phase 1 consumes from about 5% through about 55% of the time required for the entire method to be performed, but in no event should its duration be less than about 1 minute. In preferred method (A) the phase will consume about 33-42% of the total time; in method (B) about 13-23%.

The temperature of the sample should be from about 70 F. to about 120 F. during this phase.

Phase 2 The type of radiant energy to which a sample is exposed in this phase is most important. This radiant energy should have the composition Percent Ultra-violet (less than 4000 A.) 8-18 Visible (4000 A.-7000 A.) 35-60 Infra-red (greater than 7000 A.) 25-50 In preferred method (A) ultra-violet component has the wave length composition Percent 2600-3000A 4-6 3000-3400 A. 35-45 3400-4000 A 50-60 This type of radiant energy can be obtained from an RS4 lamp sold by the H. W. Gates Co.

In prefeired method (B), the ultra-violet component has the wave length composition Percent 2600-3000 A. 1 3400-3400 A 10-25 This type of radiant energy can be obtained from an RS4 and/or HlBK lamp sold by H. W. Gates Co., filtered with soda-lime glass filters about .068 inch thick.

During this phase of the method, defined broadly, the sample is exposed to a total of from about 0.2 through about 6 gram calories/cm. of ultra-violet radiation. The radiation level can be kept within this limit by varying the intensity of the radiation, the distance of the source from the sample surface and thelexposure period.

In preferred method (A), in which samples receive a second irradiation, the sample is exposed to from about 0.1 through about 0.2 gram calories/cm. and in method (B), which also receives a second irradiation, the sample is exposed to from about 1 through about 3 gram calories/ cm.

In preferred method (A) this phase usually consumes from about 15% through about 25% of the time required for the entire method to be carried out, and in preferred method (B) it usually consumes 40-45% of the time.

The temperature of the sample during this phase can be as low as 70 F. at the start and should go no higher than about 180 F. In preferred method (A) the average temperature will be from about 110 F. through about 130 F., with a maximum of about 140 F.; in preferred method (B) the average temperature will be from about 130 F. through about 160 F., with a maximum of 165 F. These temperatures evaporate the water from the samples, leaving them substantially dry. Sample temperature, as used in this context and hereafter in this specification, means the temperature of a dry black dummy sample.

At this point, one cycle of the method of the invention, described broadly, is finished and the whole process begins again. Preferred methods (A) and (B), however, have additional phases which are:

Phase 3 In preferred method (A) the sample is again kept from direct exposure to radiant energy for from about 10% through about 20% of the time required for the entire method to be performed; in method (B), for from through about During this phase, the temperature of the sample should not go below about 70 F. nor above 120 F.

Phase 4 In phase 4, the sample is again exposed to radiant energy having the same wave length composition as that in phase 2. In this phase, however, the ultra-violet radiation intensity is from about 0.2 through about 0.3 gram calories/cm? for preferred method (A) and from about 1 through about 3 gram calories/cm. for preferred method (B).

As in phase 2, the time consumed by this phase depends on the intensity of the radiant energy and the distance of its source from the sample surface. In methods (A) and (B), it will consume from about 25% through about 35% of the time required for the entire method to be performed.

In method (A) the sample temperature will be in the range of from about 115 F. through about 140 F.; in method (B) it will be from about 135 F. through about 165 F.

After they have been subjected to the simulated weathering just described, samples are sometimes diflicult to evaluate because of water-spotting. It has been found that this can be minimized if some positive means for uniformly drying the sample is provided part-way through an irradiation phase. This can be accomplished with a short blast of air blown across the sample surface, or With infra-red lamps.

When the invention is considered broadly, this positive drying step takes place during phase 2, when that phase is 2,0 30% comp te. In preferred method (B), the ying also takes place in phase 2 when it is 40-60% complete. In method (A) drying occurs in phase 4 when it is 10- 30% complete.

The number of times a samples is subjected to the method will of course depend on the degree of natural weathering one wishes to simulate. For example, if the selected preferred method gives close correlation with Florida exposure accelerated about 20 times, a six-month natural exposure can be simulated by processing a sample according to the method of the invention for 0.3 month, or about 9 days.

The size of sample to be used is a practical matter and is ordinarily selected according to need. Results obtained with the method can be interpreted any number of ways according to the needs and wishes of the user.

The claims are:

1. A method for simulating and accelerating the natural weathering of polymeric material, which method comprises repeatedly (A) wetting said material with demineralized water,

the total amount of water deposited being equivalent to about 003-015 inch of rainfall, and keeping said material wet and from direct exposure to radiant energy for from about 5% through about 55% of the time required for the method to be performed, the material being kept within the temperature range of 70120 F. during this time; and

(B) directly exposing said material to radiant energy having the composition.

Percent Ultra-violet 8-18 Visible 35-60 Infra-red 25-50 the radiation intensity being from about 0.2 through about 6 gram calories/cm. of ultra-violet radiant energy, the polymeric material being kept at a temperature of from about 70 F. through about 180 F. during the exposure, the material being subjected to drying means when the exposure to radiant energy is from 20% through about complete.

2. The process .of claim 1 wherein the drying means in step (B) is a short blast of air.

3. A method for simulating and accelerating the natural weathering of polymeric material, which method comprises repeatedly and sequentially (A) wetting said material with demineralized water,

the total amount of water deposited being equivalent to about .0030.15 inch of rainfall, and keeping said material wet and from direct exposure to radiant energy for from about 33% through about 42% of the time required for the method to be performed, the material being kept within the temperature range of 70120 F. during this time;

(B) directly exposing said material to radiant energy having the composition Percent Ultra-violet 8-18 Visible 35-60 Infra-red 25-50 the ultra-violet component having the wave length composition Percent 26003000 A. 4-6 3000-3400 A. 35-45 3400-4000 A. 50-60 the radiation intensity being from about 0.1 through about 0.2 gram calories/cm. of ultra-violet radiant energy, the polymeric material being kept at an average temperature of from about F. through about F. with a maximum of about F, during the exposure;

(C) keeping said material from direct exposure to. radiant energy for f om about 10% through about 20% of the total time required for the method to be performed, the material being kept at a temperature of from 70-120 F. during this time; and then (D) directly exposing said material to radiant energy having the same composition as in step (B) above,

6 the radiation intensity being from about 1 through about 3 gram calories/cm. .of ultra-violet radiant energy, the material being kept at an average temperature of from about 130 F. through about 160 F. with a maximum of 165 F. during the exposure,

the radiation intensity being from about 0.2 through 5 the mat rial being subje t d t a h t blast f ir about 0.3 gram calories/cm. of ultra-violet radiant when the exposure is from about 40% through about energy, the material being kept at a temperature of 60% complete;

from about 115 through about during (C) keeping the material from direct exposure to the exposure, the material being subjected to a short di en rgy f f bo t 5% through b t blast of air when the exposure is 10-30% complete.

10% of the total time required for the method to 4. A method for simulating and accelerating the natural weathering of polymeric material, which method comprises repeatedly and sequentially (A) wetting said material with demineralized water,

the total amount of water deposited being equivalent to about 003-015 inch of rainfall, and keeping said material wet and from direct exposure to radiant energy for from about 13% through about 23% of the time required for the method to be performed, the material being kept at a temperature of from 70-120 F. during this time;

(B) directly exposing said material to radiant energy having the composition be performed, the material being kept at a temperature of from 70-120 F. during this time; and then (D) directly exposing said material to radiant energy having the same composition as in step (B) above, the radiation intensity being from about 1 through about 3 gram calories/cm. of ultra-violet radiant energy, the material being kept at a temperature of from about 135 F. through about 165 F. during this time.

References Cited UNITED STATES PATENTS Percent 25 1,818,687 8/1931 Buttolph 73-150 Ultra-violet 8-18 2,434,450 1/ 1948 Williford 73-150 Visible -60 3,224,266 12/1965 Klippert 73150 Infra-red 25-50 the ultra-violet component having the wave length 30 JERRY MYRACLE Prlmary Exammer composition U.S. Cl. X.R.

Percent 73 150 2600-3000 A. 1 3000-3400 A. 10-25 3400-4000 A. 75-90 

